Reverse domain name system or rDNS is a really useful feature. But the reality is, it’s not a must to have it. It totally depends on the kind of domain you have. Answering more specifically, yes, you really need rDNS if you plan to send e-mails or provide any other service requiring DNS verification to operate.
If your domain doesn’t have such requirements, no, you don’t need to enable rDNS. Simple as that. If you want to understand properly what is rDNS and what it is for, this entire article is for you! Maybe you don’t need rDNS now, but you can need it later!